Rowling, the children’s book author behind the bestselling Harry Potter series, has announced that she has an agreement with Little, Brown to publish her first novel for grownups in the United States and Britain. The Harry Potter books were published by Scholastic in the U.S. and Bloomsbury in Britain.

Details about the new novel, including the title, subject and the release date, have yet to be announced. “Although I’ve enjoyed writing it every bit as much, my next book will be very different to the Harry Potter series, which has been published so brilliantly by Bloomsbury and my other publishers around the world,” Rowling said in a statement. Little, Brown said more information about the book would be unveiled later in the year.

An Edinburgh neighbor, crime writer Ian Rankin, recently added to the speculation about Rowling’s new book by tweeting: “Wouldn’t it be funny if J K Rowling’s first novel for adults turned out to be a crime story set in Edinburgh? My word yes.”

The question now is, can Rowling write for adults?

The fact is many parents and adult singletons read and enjoyed the Harry Potter books. And by the end of the series, the size and scope of the books had expanded–the franchise had grown up along with its readers.

“Twilight” author Stephenie Meyer helped demonstrate that today’s young adult authors can move back and forth between the world of young adult fantasy fiction and books geared towards adults. Her first book aimed at adults, “The Host,” was a New York Times bestseller and is being developed into a feature film. “I really want do a bit of everything,” Meyer told The Wall Street Journal in 2008. She added “I don’t think of it in terms of adult or young adult.”

J.R.R. Tolkien, C.S. Lewis, Ursula K. Le Guin and other top fantasy authors were able to write books that were hits with children, as well as books that were popular with adults.

The worlds of adult fiction and young adult fiction have, in many ways, been growing closer in recent years as children’s book authors explore more serious themes, including drug abuse, sexual abuse and violence.

“The Hunger Games” is nominally a book for young adults, but the violence and social commentary depicted in its pages sometimes requires a mature sensibility to truly understand. And the final book in the “Twilight” series features plenty of gore and adult situations.

Last year, Sherman Alexie, author of the award-winning young adult book “The Absolutely True Diary of a Part-Time Indian,” wrote an essay for this blog on why he believed it was necessary for kids books to grapple with difficult themes. “I can’t speak for other writers, but I think I wrote my YA novel as a way of speaking to my younger, irredeemable self,” Alexie wrote.

Rowling’s coming book may be aimed at adults, but it’s not so much a shift for her as it is an acknowledgement that the publishing industry has changed. The boundaries between the adult and and young adult market have blurred, and readers feel more freedom to go back and forth between genres.

“The freedom to explore new territory is a gift that Harry’s success has brought me,” Rowling said in a statement released today.

This time around, when adults buy Rowling’s books they won’t have to tell friends that they’re actually buying them for their kids.

Christopher John Farley is the editorial director of the Wall Street Journal blogs. Follow him on Twitter at @cjfarley